Optical information recording media as exemplified by DVD (Digital Versatile/Video Disc) and Blu-Ray discs are known as high-capacity information recording media (also called “recording media” or simply “media”) capable of high-speed information recording and reproduction. Information is recorded to and reproduced from such information recording media by using differences in the reflectances among two differing states. Because such information recording media are capable of random access as necessary and also have the advantage of being highly portable, the importance thereof has been increasing significantly in recent years.
Rewritable media capable of being rewritten multiple times, write-once media capable of being written to only once, and read-only media capable only of being reproduced can be given as types of information recording media proposed thus far. Generally speaking, a read-only medium can be composed of fewer layers than a rewritable medium or a write-once medium, making the manufacture thereof easy, and making it possible to provide such a medium at low cost. For this reason, read-only media are widely used in the distribution of digital content such as music, video, video game software, and the like.
In read-only media, sub information such as the serial number of the information recording medium is added separately from the video, music, or the like that makes up the main information in order to prevent unauthorized copying. This sub information is recorded, for example, as a barcode-shaped mark called a BCA (Burst Cutting Area) that is formed by burning a reflective layer within the information recording layer using a YAG laser.    Patent Citation 1: JP 2005-196940A